Device for optical signal transmission

ABSTRACT

An optical transfer device for transferring optical signals from a moveable part to a stationary part through an optical transfer medium in order to minimize distortions of the optical signal and increase the effective bandwidth of the signal transit path by minimizing and/or maintaining equal alternate optical signal transit paths from the transmitter to the receiver.

PRIORITY DOCUMENT

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 09/068,932, filed Sep. 2, 1998, now U.S. Pat. No.6,650,843.

FIELD OF THE INVENTION

A device for transmitting optical signals from a movable part to astationary part that increases bandwidth and decreases interference.

BACKGROUND OF THE INVENTION

The invention relates to devices for optical signal transmissionsbetween a transmitter unit and a mobile receiving unit, which areoptically coupled to each other via an optical transfer medium.

Optical systems are frequently employed to transmit data and signals.Such systems are fundamentally composed of a transmitter unit and areceiver unit, which are interconnected via an optical transfer medium.When the optical transfer medium is free space or air, an arrangementsimilar to a light barrier is achieved.

However, optical fibers, such as glass or synthetic fibers, are morefrequently used to guide the light. In both case, the length of theoptical path between the transmitter unit and the receiving unit isgenerally constant. As a result, the amplitude of the signal received inthe receiver unit is not subject to significant variations with respectto time. This facilitates a uniform transmission quality.

In the case of transmission paths that have a variable optical pathlength between the transmitter unit and the receiving unit, the signallevel at the receiver may vary due to attenuation along the opticalpath, which in turn may degrade transmission quality. In advanceddigital transmission systems, in particular, this may result in anundesirable increase of the bit error rate.

The transit time of optical signals through the optical transfer mediummay vary depending upon the distance between the transmitter and thereceiver, varying from a range of almost zero when the transmitter islocated in the immediate proximity of the receiver, up to a maximumvalue occurring when the transmitter unit is located at the farthestpoint along the optical medium from the receiver.

When the transmitter moves along the length of the medium, starting fromthe receiver up to the end of the optical medium, the transit time ofthe optical signal will increase as the transmitter moves away from thereceiver. However, in rotary systems, the transmitter initially beginstransmission at a starting point that is located at the receiver andcontinues around the circumference of the optical medium, therebyincreasing the optical path length. Once the transmitter reaches the endof the optical transfer medium, the longest optical path length, thetransmitter will then immediately transition from the end of the opticalmedium to the initial starting point to begin the process again. At theend of the optical transfer medium, there is a relatively long transittime for the optical signal to reach the receiver due to the distancetraveled by the optical signal. However, upon transition to the startingpoint, the transit time is immediately reduced to almost zero.

This abrupt difference in transit time, which may occur during thetransition, may give rise to a discontinuity in phase, restricting thebandwidth that can be transmitted, and may result in transmissionerrors.

Particularly, when optical signals are transmitted via an opticaltransfer medium shaped in the form of a closed curve, an overlapping atthe beginning and the end of the optical medium is unavoidable unless agap in transmission can be accepted in this position. That is, twosignals are superimposed in the receiver, at the beginning andsimultaneously at the end of the medium. The first signal is transmittedto the receiver without traveling along the optical path, and thereforereaches the receiver almost immediately. The second signal passes overthe entire optical path length, and thus arrives at the receiver with asubstantial delay. Both signals are now superimposed and produce anincorrect cumulative signal. As a result, the transmitted signal isdegraded. Specifically, with high frequencies where the signal transittime corresponds to one half of the period, the signal is extinguished,such that a sensible data transmission is no longer possible.

What is desired then, is an optical transmission system that providesfor transmission of optical signals from a transmitter to a receiveralong a rotatable optical coupling where the optical signal quality isnot degraded.

It is further desired to provide an optical transmission system having asignal transmission quality independent of the relative movementsbetween the transmitter and the receiver.

It is also desired to provide an optical transmission system in which nosignal overlapping occurs at the receiver to interfere with datatransmission.

It is further desired to provide an optical transmission system that issmall in size, is cost effective, and may be utilized for wide-bandsignal transmission.

SUMMARY OF THE INVENTION

These and other objects are achieved by providing a system in whichvarious optical signals arrive at the receiver concurrently. Effectivewide-band signal transmission may be achieved when optical signals areprevented from arriving at the receiver along several opticaltransmission paths of varying length, thereby creating differing transittimes. This can be accomplished, for instance, if only one signalreaches the receiver. This may be the case, for instance, on a linearpath. Independence may equally be achieved when several signals arriveat the receiver all having exactly the same optical transit times.

In one embodiment of the present invention the optical signals propagatethrough the optical transfer medium such that they arrive concurrentlyat the receiver and can thus be combined to form a single signal.Alternatively, in another embodiment of the present invention thetransfer medium is designed such that signal overlapping is avoided.

Accordingly, the optical transfer medium is severed at one location andis closed in such a manner so as to minimize reflections. Thisseparating point is located at that site of the curve from where thesignal transit times in all directions of propagation to the receiverare equal. Hence, the light arrives at the receiver along both pathswhen the transmitter is positioned above the separating point. Here, thesignal transit times are precisely equal and signal distortion will notoccur. At all other transmitter positions the light progresses along onepath to the receiver and along the other path to the separating pointwhere it is absorbed. Hence there is only one light path from thetransmitter to the receiver. This system ensures signal transmissionover a substantially larger bandwidth.

The transmitter and the receiver may be movable relative to each other.For instance, the movement may here be circular, linear or along anyother optional curve. In the event of linear travel of parts, the term“path length of travel” denotes that length of the path along which thetransmitter unit and the receiving unit may be moved relative to eachother. In the event of circular movements, it denotes the correspondingpart along the periphery of the circle. At maximum, however, it denotesthe complete circumference of the circle. The same applies also to anyother curve along which a movement may be carried out.

Pursuant to an object of the invention, in order to provide a simplelow-cost implementation of the amplifiers in the receiving unit, theoptical path length must be kept as short as possible. Of note, becausethe length of the optical transfer medium is minimized, the transmissionbandwidth is also substantially wider. This is because the transmissionbandwidth is inversely proportional to the length of the optical medium.

In one embodiment of the present invention, an optical signaltransmission system is provided between a stationary transmitter and amobile receiver that are optically coupled to each other through anoptical transfer medium such that, the transmitter transmits opticalsignals via at least one transfer medium along at least two differentoptical paths to the receiver. Both optical signal paths are designed sothat the cumulative optical path length remains approximately constantand therefore, independent of the travel. This may be achieved forinstance, when an optical transfer medium of constant length is usedthat has both ends coupled to the receiver and facilitates thecoupling-in of light from the transmitter unit at any location along thelength. The receiver is designed so that it receives the signals alongthe optical paths and generates a cumulative signal by summation that islargely independent of the travel path between the transmitter unit andthe receiving unit.

In another embodiment of the present invention, the receiver includesseveral optical receivers that convert the optical signals intoelectrical signals. At least one optical receiver is associated witheach optical path. The electrical signals of the receivers are thentotaled in an adjoining adder.

In another embodiment of the present invention, the receiver is providedwith an optical adder that adds up the optical signals of the paths.After such a summation the cumulative optical signal may be convertedinto an electrical signal whenever this will be necessary.

In a further embodiment of the present invention, with rotationalmovement between the transmitter and the receiver, the optical transfermedium may comprise an optical fiber in a circular configuration, whichis doped with a fluorescent dye, such that optical signals may becoupled into the fiber at any location along the optical signal path.

In still another embodiment of the present invention, the transfermedium is discontinuous at least at one location, from which the transittimes of the optical signals in both directions of the transfer mediumto the receiving unit are equal. The optical signals are converted intoelectrical signals by means of two optical converters at the receiverlocation. To this end, the optical transfer medium is interrupted at thereceiver location and an optical converter is inserted in each of thebranches. Transition of the optical signal from one branch into theother branch will be subjected to a strong attenuation.

The two signals of the optical converters are superimposed by means of acircuit, which may comprise an analog or digital adding circuit. In thepositioning of the separating point in the optical transfer medium, itmust be determined whether the links between the optical converters andthe adding circuit present equal transit times or differing transittimes so that equal cumulative optical signal transit times will beachieved.

In still another embodiment of the present invention, the optical mediummay be designed so that a slight overlapping of the two branches of theoptical transfer medium occurs at the separating point, or at bothseparating points if two of them are provided. This ensures reception ofoptical signals by the receiver at any point along the optical transitpath. The overlapping site must be designed so that optical signals willnot transition from one branch to the other.

In yet another embodiment of the present invention, the receivercomprises at least one optical receiver associated with an opticaltransfer medium having a length shorter than the path covered from theoptical transmitter relative to the optical transfer medium. Thetransmitter includes at least two optical transmitters spaced from eachother, along the direction of longitudinal travel, such that the lightof at least one of the optical transmitters will be coupled into theoptical transfer medium. An optical transfer medium is utilized thatencompasses only a portion of the entire path length. Several opticaltransmitters are provided to facilitate optical transmission over theentire wavelength and are arranged such that the optical transfer mediumwill be continuously illuminated by at least one optical transmitter.This makes continuous signal transmission along the entire path lengthpossible.

In another embodiment of the present invention, receivers are arrangedapproximately in the center of the segments of the optical transfermedium such that the transit times of the optical signals from both endsof the optical transfer medium are equal. In this way there is nosuperimposition of optical signals with different transit times. Theoptical transmitters are arranged such that as a transmitter leaves anoptical medium, a second transmitter approaches this optical medium onthe other side. This provision allows for continuous signaltransmission.

In another embodiment of the present invention several optical receiversare connected to an optical transfer medium. Signals of the opticalreceivers are combined with each other so that higher signal reliabilitymay be achieved through redundancy. Further, signals from severaloptical receivers may be added to achieve a higher cumulative signallevel and reduced noise. Redundant transmission also ensures that if atransmitter, an optical medium or even a receiver fails, signaltransmission may still occur along a different optical path.

In a further embodiment of the present invention, the transmitter maycomprise a position sensor for determining the particular opticaltransmitter located above the optical transfer medium. This informationis then signaled to the particular optical transmitter to activate thefull transmitting power of the particular optical transmitter.Conversely, when a transmitter is not within the range of the opticaltransfer medium, the transmitter may deactivate so as not to wastepower. A further advantage is realized by longer service life of thetransmitters and reduction of Electro-Magnetic Interference (EMI)generated by the high-power transmitters.

In still another embodiment of the present invention, severalindependent optical receivers with separate optical transfer mediums areprovided. At least as many optical transmitters are provided as thereare optical signal channels. A selector is further provided that iscontrolled by a position sensor for communicating to the selector whichone of the optical transmitters are instantaneously able to transmitsignals via the optical medium and the associated receiver to aspecified logic signal channel. Depending on the position of thetransmitter and receivers the transmission path may vary.

In a further embodiment a device is provided for transmitting opticalsignals between a stationary unit and a movable unit. The deviceincludes an optical transmitting unit that is movable along a directionof movement, and has an optical transmitter for transmitting opticalsignals. The device also includes an optical receiving unit that isstationary with respect to the optical transmitting unit, and has areceiver for receiving optical signals. The device further includes anoptical transfer medium that is optically coupled to the receiver, fortransmitting optical signals to the receiver. The optical transfermedium is severed into first and second branches of equal lengths suchthat the optical signal transit time for an optical signal along eitherof the branches from the point of severance to the receiver is equal.

In another embodiment of the present invention, a device fortransmitting optical signals between a stationary unit and a movableunit is provided including a movable unit having an optical transmittingunit for transmitting an optical signal. The device also includes astationary unit having an optical receiving unit for receiving theoptical signal. The optical receiving unit has a plurality of receivers.In addition, the device includes a plurality of optical transfer mediumsassociated with the plurality of receivers, for conducting the opticalsignals to the plurality of receivers. The optical signals aretransmitted to fewer than the plurality of receivers at any particulartime.

The invention and its particular features and advantages will becomemore apparent from the following detailed description considered withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a transmitting unit, a receivingunit and an optical medium that is severed according to an embodiment ofthe present invention.

FIG. 2 is a block diagram illustrating a transmitting unit havingmultiple transmitters, a receiving unit having multiple receivers, andan optical medium that is severed.

FIG. 3 is an illustration of a graph depicting the signals as receivedby the receivers in FIG. 2 and combined to form a cumulative signal.

FIG. 4 illustrates a transmitting unit, a receiving unit and an opticalmedium that is severed according to the embodiment illustrated in FIG.1.

FIG. 5 illustrates a transmitting unit, receiving unit having tworeceivers, and an optical medium that is severed in two locationsaccording to the embodiment illustrated in FIG. 1.

FIG. 6 is a signal/transit time diagram according to the embodimentillustrated in FIG. 5

FIG. 7 is a block diagram illustrating a transmitting unit havingmultiple transmitters, a receiving unit, and an optical medium that issevered.

FIG. 8 is a block diagram illustrating a transmitting unit havingmultiple transmitters, and a receiving unit having multiple receiverseach associated with an optical medium.

FIG. 9 is a block diagram according to FIG. 5 illustrating atransmitting unit, and a receiving unit having multiple receivers eachassociated with an optical medium.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of one advantageous embodiment of theinvention, which generally comprises a transmitting unit 10, an opticalmedium 12, and a receiving unit 14. The transmitting unit 10 includes atleast one transmitter 16, which relays optical information and/or energyvia the optical medium 12 to the receiving unit 14. The optical medium12 presents a constant length and is severed at one point so as tocreate two equal portions.

The transmitting unit 10 and the receiving unit 14 may be movablerelative to each other. Generally one of the units, either thetransmitting unit 10 or the receiving unit 14, is stationary and theother unit is movable. The movement may be either circular or linear, oralong any other optional curve.

The transmitter 16 transmits optical signals to the receiving unit 14along either one of the portions of the optical medium 12, except whenthe transmitter is located above the severance point, in which case,optical signals will travel along both portions of the optical medium 12to the receiving unit 14. However, because the two portions of theoptical medium 12 are equal in length, the two optical signals arrive atthe receiving unit 14 at the same time.

The receiving unit 14 may include one or more receivers for receivingthe optical signals. In addition, the optical medium 12 may include oneor more severance points.

The severance points are formed in such a manner that reflection ofoptical signals along the optical medium 12 is minimized. Therefore, theseverance points are designed to strongly attenuate optical signals thatcome into contact with them so that the optical signals are nottransmitted into another portion of the optical medium 12, and are notreflected back into the same portion of the optical medium 12 therebycausing signal distortion at the receiving unit 14.

FIG. 2 is an illustration of another embodiment of the presentinvention. A transmitting unit 20 is shown having two transmitters 22and 24. In addition, an optical transfer medium is provided having twoequal portions 26 and 28, corresponding to transmitters 22 and 24respectively. A receiving unit 34 is further illustrated having tworeceivers 30 and 32 located therein. Receivers 30 and 32 are connectedat one end of the optical transfer mediums 26 and 28 respectively, forreceiving the optical signals and/or energy from transmitters 22 and 24.This facilitates the coupling-in of optical signals and/or energy fromtransmitters 22 and 24 at any location along the length of opticaltransfer mediums 26 and 28.

Both transmitters 22 and 24 transmit the same informationsimultaneously. Both optical signal paths are provided so that thecumulative optical path length, i.e. the sum of the optical path lengthfrom transmitter 22 to receiver 30 and from transmitter 24 to receiver32, remains approximately constant and therefore, independent of thetravel. The receiving unit 34 is designed so that it receives theoptical signals and/or energy along optical transfer mediums 26 and 28and generates a cumulative signal by summation that is largelyindependent of the travel path between the transmitting unit 20 and thereceiving unit 34.

FIG. 3 illustrates, the effects of the addition of two signals,corresponding to the system on the amplitude of the cumulative signal.The position of the transmitter relative to the receiver is plottedhorizontally in the diagram. When the transmitter unit is in the leftposition, for example, the signal level 44 in the first receiver 30 islower than the signal level 42 in the second receiver 32, due to thelong optical path. When the transmitting unit 20 is moved, for instance;to the right, the signal level in the first receiver 30 rises, while thesignal level in the second receiver 32 falls. In sum, the graph of thecumulative signal 40 is an approximation. This graph is approximatelyindependent of the position.

FIG. 4 shows an embodiment of the invention consisting of a transmittingunit 50 and a receiving unit 52. The units are interconnected by anoptical medium 54 of any kind desired, which is shaped to constitute aclosed curve. The closed curve illustrated in FIG. 4 is shown as anirregular shape, however the curve may comprise any closed curveincluding for instance, but not limited to; a circle, an ellipse, or anyclosed shape. The transmitting unit 50 is adapted to be moved relativeto the receiving unit 52 along this curve. In FIG. 4 the transmittingunit 50 is illustrated as the movable portion while the receiving unit52 is depicted as the stationary portion. However, it is contemplatedthat receiving unit 52 may also comprise the movable portion while thetransmitting unit 50 is stationary. Further, it is also contemplatedthat both the transmitting unit 50 and the receiving unit 52 may bemoveable relative to each other. What is important here is the mutuallyrelative movement. Likewise, the receiving unit 52 may move togetherwith the optical medium 54 relative to the transmitting unit 50.

ST1 defines a point where the optical medium 54 is discontinuous orinterrupted. The discontinuity or interruption of the optical medium 54at point ST1 is designed such that optical signals propagating throughthe optical medium 54 that reach point ST1 will be largely absorbed andattenuated rather than being reflected back down the optical medium 54.Point ST1 is located in the optical medium such that the length of thesevered optical medium is halved. That is, the length of the opticalmedium 54 from point ST1 to the receiving unit 52 is equal in bothdirections. This is desirable because it will facilitate having equaltransit times for optical signals in both branches of the curve.

FIG. 5 is a further embodiment of the present invention. In thisembodiment, a transmitting unit 60 is provided, having a transmitter 61located therein, along with a receiving unit 62 for receiving thetransmitted signal. In addition, optical medium 64 is provided and isdiscontinuous or interrupted at two points ST1 and ST2 forming twobranches (64A and 64B) of the optical medium 64 of equal length. Asdescribed in FIG. 4, an optical signal interacting with ST1 or ST2 willbe subjected to a strong attenuation to eliminate or minimizereflections back down the branch and/or eliminate transmission into theother branch of the optical medium 64.

Two optical converters 66 and 68 are provided in receiving unit 62.Optical converters 66 and 68 are each associated with branches (64A and64B) of optical medium 64 respectively. The optical medium 64 isinterrupted at point ST2 between optical converters 66 and 68 such thatoptical signals cannot be transmitted from one branch of the curve intothe other one.

The received optical signals are converted into electrical signals bymeans of optical converters 66 and 68.

The two electrical signals generated by optical converters 66 and 68 arethen superimposed by means of a circuit, which may comprise an analog ordigital adding circuit. It is desired to form a cumulative opticalsignal with the analog or digital adding circuit, therefore, care mustbe taken in positioning the separating points ST1 and ST2 in the opticaltransfer medium such that, the optical medium 64 presents two branchesof equal length so that the transit times of the optical signals areequal.

FIG. 6 clearly shows the effects of the addition of signals withdifferent transit times. Curve (a) corresponds to the original signal.The signal in curve (b) presents only slight delay relative to signal(a). The addition or superimposition of the two curves results in asignal corresponding to curve (c). This signal presents only slightdistortions and is easy to evaluate in the receiving unit. In the eventof a fairly strong delay of the second signal, e.g., the one representedby curve (d), an entirely different situation occurs. The result isplotted in curve (e). The development of the curve can no longer beunambiguously interpreted.

Evaluation becomes particularly complicated in an arrangement thatcorresponds to the prior art as the signal shape may vary over wideranges (i.e., as a function of the position of the transmitter relativeto the receiver). For instance, the signal shape may have any shapebetween curves (c) and (d) as a function of the position.

FIG. 7 is a view of a further embodiment of the invention. In thisembodiment, transmitting unit 70 and receiving unit 72 are provided,with receiving unit 72 being connected to optical medium 74.Transmitting unit 70 includes several, optical transmitters (76A, 76B,76C, 76D). Some of the optical transmitters are illustrated (76A, 76B,76C, 76D), and are designed so that they are suitable for couplingoptical data into optical medium 74. Although four optical transmitters(76A, 76B, 76C, 76D) are illustrated, any number may be utilized.

Optical transmitters (76A, 76B, 76C, 76D) are arranged such that atleast one respective transmitter will couple an optical signal intooptical medium 74 at any given time (t). The position sensor 78determines the position (p) of the optical transmitters (76A, 76B, 76C,76D). Once it is determined that a particular one of the opticaltransmitters (76A, 76B, 76C, 76D) is positioned above the optical medium74 at a particular time t, that particular optical transmitter isactivated to transmit an optical signal, while the remaining opticaltransmitters are off. The optical transmitters (76A, 76B, 76C, 76D) aretherefore cycled on and off based upon their determined position withrespect to the optical medium 74.

FIG. 8 depicts still another embodiment of the present inventionincluding; transmitting unit 80, receiving unit 82 and an optical mediumcomprising three branches 84A, 84B and 84C. Receiving unit 82 is furtherprovided with receivers 86A, 86B and 86C, corresponding to opticalmediums (84A, 84B, 84C) respectively. Transmitting unit 80 includestransmitters 88A, 88B, 88C and 88D. In addition, transmitting unit 80 isprovided with a selector switch 90 and a position sensor 92. Asdescribed in FIG. 7, the position sensor 92 determines the position ofthe transmitters (88A, 88B, 88C, 88D) with respect to the opticalmediums (84A, 84B, 84C). The selector switch 90 then switches thetransmitters (88A, 88B, 88C, 88D) on and off based on information fromthe position sensor 92, establishing a logic relationship between thetransmitters (88A, 88B, 88C, 88D) and the receivers (86A, 86B, 86C).

In FIG. 8, four transmitters (88A, 88B, 88C, 88D) and three receivers(86A, 86B, 86C) are illustrated. However, any number and combination oftransmitters and receivers may be utilized. In this particularillustration, one more transmitter is illustrated than receiver so thatefficient transmission of signals from the respective transmitters (88A,88B, 88C, 88D) to respective receivers (86A, 86B, 86C) may occur at timet. As described in FIG. 7, the position sensor 92 may cycle transmitters(88A, 88B, 88C, 88D) on and off based upon their position relative tooptical mediums (84A, 84B, 84C) at time t.

FIG. 9 is a block diagram according to FIG. 5 of the present invention.Here transmitting unit 60 is provided including transmitter 61. Inaddition, receiving unit 62 is provided along with optical mediums 64Aand 64B. The optical mediums (64A and 4B) are each associated withreceivers 66 and 68 and are located in receiving unit 62 respectively.In this case, transmitter 61 transmits optical signals through aparticular optical medium (64A and 64B) to a particular receiver (66,68) at any particular time t.

In this block diagram, a single transmitter 61 is illustrated with tworeceivers (66 and 68) according to FIG. 5. However, more than onetransmitter may be utilized, and any number of receivers may beutilized. However, in any event, the optical signal transmitted bytransmitter 61 is received by less than all the receivers (66, 68), andthe optical transmission path from the transmitter 61 to the respectivereceiver (66, 68) is shortened thereby reducing the signal transit time.

The relative movement of the transmitting units 10, 20, 60, 70 and 80illustrated in FIGS. 1, 2, 7, 8 and 9 may comprise either linear orrotational movement (i.e. through a full 360 degrees or any fractionthereof).

Although the invention has been described with reference to a particulararrangement of parts, features and the like, these are not intended toexhaust all possible arrangements or features, and indeed many othermodifications and variations will be ascertainable to those of skill inthe art.

1. A device for transmitting optical signals between parts movable in relation to each other comprising: an optical transmitting unit having at least two transmitters for transmitting optical signals, said optical transmitting unit being movable along a path of movement; an optical receiving unit having a receiver for receiving the optical signals; and an optical transfer medium for optically coupling said optical transmitting unit to said optical receiving unit; wherein the length of said optical transfer medium is shorter than the path of movement along which said optical transmitting unit travels; and the at least two optical transmitters are spaced from each other along the path of movement of said transmitting unit such that optical signals from at least one of the optical transmitters is coupled into said optical transfer medium at any particular time.
 2. The device according to claim 1, wherein said optical receiving unit is centrally disposed along a length of said optical transfer medium such that transit times of optical signals from a first end and a second end of said optical transfer medium to said optical receiving unit are equal.
 3. The device according to claim 2, wherein said at least two optical transmitters are spaced from each other such that when one of said optical transmitters advances beyond the first end of said optical transfer medium owing to movement of said optical transmitting unit along the path of movement, the second optical transmitter approaches the second end of said optical transfer medium, hence continuing a transmission of optical signals.
 4. The device according to claim 3, wherein said optical transmitting unit further comprises a position sensor for determining which one of said transmitters is in a position to be coupled with said optical transfer medium and for transmitting an activation signal to said one transmitter to activate a full transmitting power thereof.
 5. The device according to claim 1, for transmitting optical signals from said transmitting unit to said receiving unit along a plurality of logical signal channels, said device further comprising: a plurality of optical transfer mediums associated with a plurality of receivers, each optical transfer medium being assigned to a particular logical signal channel; a position sensor, for determining which of one said optical transmitters is able to transmit optical signals to an optical receiver assigned to a particular logical signal channel via the optical transfer medium associated with said optical receiver, at any particular time; and a selector switch, controlled by said position sensor for switching any one of the plurality of transmitters to any one particular logical signal channel; wherein said position sensor communicates to the selector switch which of the plurality of transmitters is able to transmit optical signals to a particular logical channel at any particular time.
 6. The device according to claim 1, wherein said optical transfer medium is selected from the group consisting of: a light-conducting fiber, a light-conducting fiber doped with a fluorescent dye, a shaped light-conducting body and a light-conducting liquid.
 7. The device according to claim 1, wherein said optical transfer medium is formed in a linear configuration.
 8. The device according to claim 7, where the path of movement is linear movement between said optical transmitting unit and said optical receiving unit, and said linear configuration is formed in parallel with the direction of the linear movement.
 9. A device for transmitting optical signals between parts movable in relation to each other comprising: a transmitting unit, movable along a direction of movement, and having a plurality of transmitters for transmitting optical signals; a receiving unit, having a plurality of receivers for receiving optical signals; a plurality of optical transfer mediums associated with said plurality of receivers; wherein the plurality of transmitters are greater in number than the plurality of receivers such that not every transmitter is coupled to every receiver at any particular time.
 10. The device according to claim 9 wherein said transmitting unit includes a position sensor for sensing the position of said plurality of transmitters in relation to said plurality of receivers such that any particular transmitter may transmit optical signals to any particular receiver at any particular time.
 11. A device for transmitting optical signals between parts movable in relation to each other comprising: a movable unit, with an optical transmitting unit associated therewith for transmitting an optical signal; a stationary unit, with an optical receiving unit associated therewith for receiving the optical signal, the optical receiving unit having at least two receivers; an optical transfer medium associated with each of the at least two receivers, for conducting the optical signals to the at least two receivers respectively; wherein the transmitting unit is coupled to one of the at least two receivers at any particular time such that the optical signals are transmitted to fewer than all of the at least two receivers at any particular time.
 12. The device according to claim 11 wherein the transmitting unit has at least two transmitters for transmitting optical signals and the receiving unit has at least three receivers for receiving the optical signals.
 13. The device according to claim 12 wherein the total number of transmitters is fewer in number than the total number of receivers.
 14. The device according to claim 13 wherein the transmitters are spaced and located in the optical transmitting unit along a direction of movement.
 15. The device according to claim 14 wherein the direction of movement is linear.
 16. The device according to claim 14 wherein the direction of movement is along a closed curve. 